1. Field of the Invention
The invention relates in general to a low-leakage Input-Output (IO) circuit and associated apparatus, and more particularly to an IO circuit and associated apparatus applying an internal switch circuit to disconnect an impedance path of a pull-up resistor when a power supply is powered off, so as to effectively reduce power leakage.
2. Description of the Related Art
Electronic devices are one of the most crucial hardware foundations in modern information based society. An electronic device usually comprises integrated circuits and chips of different functions, and the integrated circuits and chips exchange signals with one another to yield a consolidated overall function of the electronic device.
In a chip, IO circuits and corresponding pads (e.g., signal IO pads) are means for chips to connect to external circuits (e.g., another chip or a printed circuit board) to form a signal exchange interface of the chip. To satisfy requirements of some signals, terminal resistors such as a pull-up resistor is provided in a pad or an IO circuit to maintain appropriate signal levels or to serve to match impedance of a corresponding signal path. When the chip is powered off, the pad of the chip continuously draws electric power from an external circuit connected to the chip via its impedance in the event that the external circuit keeps transmitting signals to the chip. For the external circuit, the pad of the chip simulates a leakage path through which electric power is continuously lost. Therefore, in certain signal exchange specifications, not only impedance of predetermined values (e.g., a pull-up resistor) are required for some pads of a signal exchange interface, but also leakage tolerance is regulated for the pads to limit leakage of the pads. For example, according to High-Definition Multimedia Interface (HDMI) specifications, strict standards are specified for Consumer Electronic Control (CEC) pins—it is therefore essential to have a satisfactory low-leakage pull-up resistor to achieve such leakage standards.